A comprehensive review of the preparation of alcohols by catalyst hydrogenation of carbonyl compounds, and particularly of ketones, aldehydes and derivatives thereof, can be found in Houben-Weyl, Methoden der Organischen Chemie (Methods of Organic Chemistry), Georg Thieme Verlag Stuttgart-New York 1984, volume VI/1 pages 9 to 111.
DE-AS 1,227,882 describes a two- or three-stage hydrogenation of unsaturated aldehydes in the gas phase, in which the first stage is conducted in the presence of a copper catalyst while the second stage employs a palladium catalyst or a supported nickel catalyst. In the third stage, a palladium catalyst is used.
DE-AS 1,276,618 relates to a two-stage hydrogenation of saturated and unsaturated aldehydes in the gas phase, in which the reaction first takes place on a copper/nickel catalyst and then on a nickel and/or palladium catalyst.
For preparing 2-ethylhexanol from propylene, DE 3,530,839 Al describes a two-stage hydrogenation of 2-ethylhexenal, in which the reaction is first conducted in the gas phase using a copper catalyst and then in liquid phase using a nickel-containing catalyst.
The process processes describes above for preparing alcohols leave something to be desired, however as far as conversion and/or the selectivity of the catalytic hydrogenations is concerned. The relatively long reaction times lead to correspondingly low outputs at high reaction temperatures, particularly in the second stage. Further, the valuable product can, in most cases, be recovered from the reaction product by means of distillation in the desired purity, only at great expense.